1. Field of the Invention
The present invention relates to a concentration measuring device for measuring the concentration of a developer liquid in an electrographic printer.
2. Description of the Related Art
FIG. 1 shows a schematic diagram illustrating a conventional electrographic printer.
Referring to FIG. 1, an electrographic printer includes: a photosensitive belt 14 which is supported by a driving roller 11, a steering roller 12 and a backup roller 13, and circulates in a closed loop; four development devices 17a through 17d; and a transfer roller 25 which rotates in contact with the backup roller 13. The surface of the photosensitive belt 14 is charged by a corona charger. Laser scanning units 18a through 18d are installed in the vicinity of the respective development devices 17a through 17d, and the laser beams from the laser scanning units 18a through 18d scan the surface of the photosensitive belt 14, and change the potential of the surface of the photosensitive belt 14 to form an electrostatic latent image. The photosensitive belt 14 formed with the electrostatic latent image is sequentially developed by the development devices 17a through 17d containing respective developer liquids of black, yellow, cyan and magenta colors, and accordingly a color image is formed on the photosensitive belt 14. In this case, a cleaning roller 23 removes a carrier from the color image formed on the photosensitive belt 14, and heating rollers 24 evaporate the carrier on the surface of the cleaning roller 23.
The developed color image on the photosensitive belt 14 is transferred to the transfer roller 25, and the color image transferred to the transfer roller 25 is transferred to a paper 27 by the difference of the surface energies. The color image transferred to the paper 27 is firmly fixed to the paper 27 by a fixing roller 26. Once printing is completed in this manner, an eraser 15 completely removes the charge on the photosensitive belt 14, and prepares the photosensitive belt 14 to form a new electrostatic latent image.
The developer liquids contained in the development devices 17a through 17d are mixtures of respective toners and a carrier, the toners are stored in toner containers 19a through 19d and are supplied to mixing containers 21a through 21d by pumps 20a through 20d, and the carrier is stored in a carrier container 28 and is supplied to the mixing containers 21a through 21d. The toners and the carrier supplied to the mixing containers 21a through 21d are mixed to have an appropriate concentration, and are supplied to the development devices 17a through 17d by pumps 22a through 22d, respectively.
In the printer as described above, the concentrations of the developer liquids supplied to the respective development devices 17a through 17d must be maintained to be constant, and therefore the mixing ratios of the toners and the carrier which are supplied from the toner containers 19a through 19d and the carrier container 28 are maintained within an appropriate range.
In order to decide whether the mixing ratio of the toner and the carrier is appropriate, the concentration of the developer liquid must be measured. However, since an appropriate device capable of measuring the concentration of the developer liquid is not provided in a conventional printer, it is impossible to know whether the developer liquid is at an appropriate concentration. Therefore, the tones of a color image are abnormal when the concentrations of the developer liquids are irregular.